1. Field
Embodiments of the present invention relate to an energy storage system and a controlling method thereof, and, more particularly, to an energy storage system and a controlling method thereof, which enables the frequency of power flowing in an electric-power system to be continuously regulated.
2. Description of the Related Art
As environmental destruction and resource exhaustion are becoming a serious problem, there is a rising interest in a system that may store energy and efficiently utilize the stored energy. Likewise, there is a rising interest in new renewable energy that never or scarcely causes pollution (e.g., causes little pollution) during power generation. An energy storage system may be a system that uses the new renewable energy, a battery system and an existing electric-power system in conjunction with each other.
Such an energy storage system is configured to include a battery system that stores power, a power conversion system that properly converts power of the battery system, a power generation system, and an electric-power system. The energy storage system then supplies the converted power.
When the electric-power system is in an abnormal state, for example, a power failure occurs, the energy storage system may perform an uninterruptible power supply (UPS) operation. Further, when the frequency is changed depending on a change in consumption of power flowing in the electric-power system, the energy storage system may perform frequency regulation to maintain a desired frequency by charging or discharging power stored in the battery system, thus allowing a frequency to be kept constant or substantially constant.
When the energy storage system is operated to regulate the frequency, it is required to continuously and randomly charge or discharge the battery system. However, when the battery system comes into a full charge state or a full discharge state due to the accumulation of the charging or discharging operations, the charging or discharging operation may be stopped. In this case, the state of charge (SOC) of the battery system should be regulated to 50% again and then the charging or discharging operation to perform the frequency regulation may resume, thus causing an inconvenience.